A major problem in, inter alia, processors and harvesters of the type used in mechanised forestry is the difficulty of effecting reliable feeding of individual stems past the limbing tools which serve to delimb the stems. Thus, conventional stem feeding devices often slip against the stem if the resistance to delimbing is great. The slipping tendency is especially pronounced in periods of sap flow when the adherence of the bark to the stemwood is extremely low.
The spiked rollers previously used for these feeding operations have now been abandoned for the reason that they cause unacceptable damage to the stemwood, thereby deteriorating the wood quality. Instead of such spiked rollers, use has been made of large diameter rubber wheels in order to establish a large contact surface between the stem and the feeding units. However, these arrangements suffer from the serious disadvantage that two wheels of large diameters are extremely space-requiring, which makes the processor or harvester unwieldy and difficult to operate. To solve this problem, it has also been attempted to use, for the feeding units, endless bands which are passed around two spaced-apart wheels and urged with one side against the stem, but also these band feeders have been unsatisfactory because only a point load is achieved at the two wheels and, between these wheels, a diffuse and weak band engagement pressure which has but a marginal effect.
WO85/05589 (PCT/FI85/00046) discloses an arrangement in which it is attempted to solve the above-mentioned problems by using an endless chain member which is carried by driving and idling wheels. Between these wheels, the chain member is carried by slideways to ensure that the chain member engages the stem. The chain member is composed of standard roller chains which, however, entail a number of disadvantages. To ensure that the chain member will operate as intended, it has been formed with a large number of links in the longitudinal direction, and the driving and idling wheels have a comparatively large radius. Furthermore, the chain member has been trebled with laterally offset links, which means that the chain member has a very large number of hinges. The outer parts of the chain member slide on semicircular separate slideways in the area of the driving wheel, and these slideways have a peripheral radius of the same size as the effective radius of the driving wheel. A chain member of this type requires much maintenance because the hinges wear makes frequent retensioning necessary. Chain members of this type are subject to intense wear, and even a low wear causes considerable changes in the length of the chain because of the large number of parts subject to wear. This is the case also if the chain member, like other roller chains, is lubricated and cleaned as often as required. Furthermore, the load on the stem must be restricted because of the comparatively slender dimensions of the chain and the resultant slender dimensions of the feeder frame parts cooperating with the chain. Finally, it should be noted that the friction losses in a chain system of this type will be large even if the system has been adequately lubricated and cleaned, and the need for frequent lubrication and cleaning constitutes a further serious disadvantage.